1. Field of the Invention
The present invention relates to a voice communication terminal's noise-canceling device that cancels only specified frequency components of a voice signal.
2. Description of the Related Art
With a voice communication terminal such as a telephone, there are cases where the speaker is calling under conditions where there is a lot of noise or where noise is mixed into the phone line. In order to prevent the caller's voice from becoming difficult to hear due to such noise, a filter provided in a phone is known that allows only signals of a specified frequency band to pass through. This filter is designed to perform processing on the caller's voice in order to make it clear. In this case, the filter used in the phone is provided with only fixed qualities or characteristics that allow only, for example, the frequency band of a person's voice to pass through (see Official Gazette of JP-A No. 05-252253).
Meanwhile, another device is known where noise can be detected, noise such as that mixed into the electrical waves of phone lines or wireless radio or noise that enters the microphone provided in the phone device. The device calculates the filter coefficient in accordance with the detected noise level. It is designed so that, by setting this coefficient in the digital filters, the filter qualities of those digital filters can be appropriately changed and the caller's voice is clarified (see Official Gazette of JP-A No. 07-235969).
Nonetheless, there are various frequency bands for both human voices and noise. Accordingly, with only a single filter such as in the above-described first invention, where the frequency qualities are fixed, it is difficult to obtain a caller's voice that is clear under all conditions.
Also, in a phone device such as in the second of the above-described inventions, when a filter coefficient is calculated in accordance with a detected noise level and the qualities of the digital filter are changed appropriately, calculation of the filter coefficient performed in order to improve the problematic point of the first invention takes time. As a result, a delay is generated in the time it takes for the speaker's voice to be outputted from the speaker of the phone device. When communicating by voice, if the delay of the callers' voices becomes great, the tempo of the conversation shifts and the conversation itself becomes difficult. This is especially the case with IP phones that use a Voice-over Internet Protocol (VoIP) where there are inherently lags or delays that accompany voice compression and decompression processing, delays caused by packetization, and delays generated when the IP packet passes through a network. Further increases in lag time caused by other factors are not preferable in the real-time qualities required in voice communication.
The present invention was made in point of the above, and provides a noise-canceling device of a voice communication terminal that can obtain the desired filter qualities in real-time without calculating filter coefficients.